Method for implementing Vptat multiplier in high accuracy thermal sensor

Abstract

A method for determining temperature of a chip, includes generating a first voltage and a second voltage using a pair of bipolar-junction transistors, and generating a third voltage using another bipolar-junction transistor. When a most recent bit of a bitstream is a logic-zero, the difference between the first and second voltages is sampled using a switched-capacitor input-sampling circuit, and a difference between the first and second voltages is integrated, to produce a proportional-to-absolute-temperature voltage. The proportional-to-absolute-temperature voltage is quantized to produce a next bit of the bitstream. When the most recent bit of the bitstream is a logic-one, the third voltage is sampled using the switched-capacitor input-sampling circuit, and the third voltage is integrated, to produce a complementary-to-absolute-temperature voltage. The complementary-to-absolute-temperature voltage is quantized to produce a next bit of the bitstream. The bitstream is filtered and decimated to produce an output code representative of the temperature of the chip.

The invention claimed is: 
     
       1. A method for determining a temperature of an integrated circuit chip, comprising:
 generating a first voltage and a second voltage using a pair of bipolar junction transistors; 
 generating a third voltage using a further bipolar junction transistor; 
 when a most recent bit of a bitstream is a first logic state,
 sampling a difference between the first voltage and the second voltage using a switched capacitor input sampling circuit and integrating the difference between the first voltage and the second voltage to produce a proportional-to-absolute-temperature voltage; and 
 quantizing the proportional-to-absolute-temperature voltage to produce a next bit of the bitstream; 
 
 when the most recent bit of the bitstream is a second logic state,
 sampling the third voltage using the switched capacitor input sampling circuit and integrating the third voltage to produce a complementary-to-absolute-temperature voltage; and 
 quantizing the complementary-to-absolute-temperature voltage to produce a next bit of the bitstream; 
 
 filtering and decimating the bitstream to produce an output digital code representing the temperature of the integrated circuit chip. 
 
     
     
       2. The method of  claim 1 , wherein the integrating the difference between the first voltage and the second voltage is performed a first predetermined number of times to apply a first scaling factor to the proportional-to-absolute-temperature voltage. 
     
     
       3. The method of  claim 1 , wherein the integrating the third voltage is performed one time to apply a second scaling factor to the complementary-to-absolute-temperature voltage. 
     
     
       4. The method of  claim 1 , wherein the filtering and decimating of the bitstream includes low pass filtering and decimation to reduce the bitstream to the output digital code. 
     
     
       5. The method of  claim 1 , wherein the output digital code is used to calculate the temperature of the integrated circuit chip using an equation Temperature=A*μ+B, with A and B being constants, and u representing a ratio indicative of the sampled and integrated voltages with respect to a reference voltage. 
     
     
       6. The method of  claim 1 , further comprising generating control signals in response to the bits of the bitstream, wherein the control signals control switching actuation of switches of the switched capacitor input sampling circuit. 
     
     
       7. A method for determining a temperature of an integrated circuit chip, comprising:
 when a most recent bit of a bitstream is a first logic state, causing sampling and integration of a difference between a base-emitter voltage of a first bipolar junction transistor and a base-emitter voltage of a second bipolar junction transistor to thereby produce a voltage proportional-to-absolute temperature; and 
 when the most recent bit of the bitstream is a second logic state, causing sampling and integration of a base-emitter voltage of a third bipolar junction transistor to thereby produce a voltage complementary-to-absolute temperature; and 
 filtering and decimating the bitstream to produce a signal indicative of a temperature of the integrated circuit chip. 
 
     
     
       8. The method of  claim 7 , wherein the sampling and integration of the difference between the base-emitter voltage of the first bipolar junction transistor and the base-emitter voltage of the second bipolar junction transistor is performed a first given number of times;
 and wherein the sampling and integration of the base-emitter voltage of the third bipolar junction transistor is performed a second given number of times. 
 
     
     
       9. The method of  claim 8 , wherein the first given number of times is an integer greater than 1; and wherein the second given number of times is one time. 
     
     
       10. The method of  claim 8 , wherein the first given number of times is a first integer greater than 1; and wherein the second given number of times is a second integer greater than 1. 
     
     
       11. The method of  claim 10 , wherein the second given number of times is less than the first given number of times. 
     
     
       12. A temperature sensing circuit for an integrated circuit chip, comprising:
 first and second bipolar junction transistors configured to generate first and second voltages; 
 a third bipolar junction transistor configured to generate a third voltage; 
 a sampling circuit operatively connected to the first, second, and third bipolar junction transistors and configured to sample voltages therefrom; 
 an integrator coupled to the sampling circuit and configured to integrate voltages received therefrom to produce a proportional-to-absolute-temperature voltage when a current bit of a bitstream is at a first logic value but to produce a complementary-to-absolute-temperature voltage when the current bit of the bitstream is at a second logic value; 
 a quantization circuit coupled to the integrator and configured to generate the bitstream from the integrated voltages; and 
 a low-pass filtering and decimation circuit configured to convert the bitstream to an output digital code representing temperature of the integrated circuit chip. 
 
     
     
       13. The temperature sensing circuit of  claim 12 , further comprising a control signal generator configured to produce control signals that control operation of the sampling circuit based on values of the bitstream. 
     
     
       14. The temperature sensing circuit of  claim 12 , wherein the sampling circuit includes matched capacitors with equal capacitance values. 
     
     
       15. The temperature sensing circuit of  claim 12 , wherein the integrator is a fully differential amplifier with integration capacitors connected between its inputs and outputs, and is configured to operate in a sampling phase and an integration phase based on control signals corresponding to a logic state of the bitstream. 
     
     
       16. The temperature sensing circuit of  claim 12 , wherein the quantization circuit includes a sigma-delta modulated analog to digital converter configured to operate based on the integrated voltages from the integrator. 
     
     
       17. The temperature sensing circuit of  claim 12 , wherein the sampling circuit is a switched capacitor input sampling circuit. 
     
     
       18. The temperature sensing circuit of  claim 12 , further comprising circuitry configured to use the output digital code to calculate the temperature of the integrated circuit chip using an equation Temperature=A*μ+B, with A and B being constants, and μ representing a ratio indicative of the sampled and integrated voltages with respect to a reference voltage. 
     
     
       19. The temperature sensing circuit of  claim 12 , further comprising circuitry to cause the sampling and integration of a difference between a base-emitter voltage of the first bipolar junction transistor and a base-emitter voltage of the second bipolar junction transistor to be performed a first given number of times to produce the proportional-to-absolute temperature voltage, and to cause the sampling and integration of a base-emitter voltage of the third bipolar junction transistor to be performed a second given number of times to produce the complementary-to-absolute temperature voltage. 
     
     
       20. The temperature sensing circuit of  claim 19 , wherein the first given number of times is an integer greater than 1; and wherein the second given number of times is one time. 
     
     
       21. The temperature sensing circuit of  claim 19 , wherein the first given number of times is a first integer greater than 1; and wherein the second given number of times is a second integer greater than 1. 
     
     
       22. The temperature sensing circuit of  claim 19 , wherein the second given number of times is less than the first given number of times.